Many types of aircraft use ram air flow for various purposes such as in a cooling system for aircraft auxiliary heat loads. In other words, in aircraft cooling systems, a heat exchanger can utilize an air flow to remove heat from various heat loads such as lubricating systems, electrical systems and other heat generating sources. A readily available source of air flow is through the engine compartment or ram air flow. The air flow also might be used in the environmental system of the aircraft, such as for conditioning the air and passing the conditioned air through the pressurized cabin of the aircraft at a suitable ventilation rate. Heat exchangers often are used in the air conditioning system. In most systems of this type, the cabin air, after circulation within the cabin, simply is discharged directly overboard.
When the aircraft is in flight, the movement of the aircraft creates a sufficient source of ram air flow which can be used for purposes as described above. However, when the aircraft is on the ground or is moving at low Mach operation, a fan may have to be utilized to augment the air flow and provide a source of air to the heat exchanger systems. Most often, separate air ducts are used for the ram air flow and the forced fan air flow, or complicated partitioning means are provided within an engine compartment, for instance, to separate the two flow paths. This not only increases costs, but it is detrimental to all efforts of providing compact packaging for components in modern aircraft.
This invention is directed to an improved ram air flow system which utilizes a simple, single air duct for both types of air flow.